Embodiments of the inventive concept described herein relate to a technique for estimating information about an image depth, and more particularly, relate to a method and an apparatus which are capable of estimating information about a depth by installing a birefringent medium such as a birefringent flat plate in front of one camera.
Image depth estimation is very useful for many applications such as computer graphics, robotics, autonomous vehicles, augmented reality, etc. A general stereo or multi-view stereo image technique requires at least two cameras to estimate disparity, so that an additional cost and a large form factor are incurred. Although any other schemes using a single camera have been proposed, those schemes have other drawbacks and require additional hardware which obstructs applications in all scenarios. For example, a scheme is dependent on a structured light and a biprism stereo diminishes a valid sensor resolution by half. The trade-off between a spatial resolution and the number of captured images is one of main limitations of an optical-field depth image.
A reflection based stereo requires a scene imaged through a double-sided half-mirror plate inclined to the right. Depth-from-defocus (DFS) techniques may require shallow depth-of-field to improve depth sensitivity and depth ambiguity may occur due to a low frequency signal. Because previous refraction based stereo techniques require a plurality of input images, the refraction based stereo techniques are suitable to still scenes.
Birefringence is the optical property of anisotropic transmittable material, whereby incident light is split into two rays, that is, ordinary and extraordinary rays, causing the birefringence. Such a phenomenon including information about overlapping of scenes allows a single image to be captured from depth information.
However, there are many problems to be technically solved to estimate a depth from birefringence. First, although several studies are focused on birefringence about a computer graphic simulation, any birefringent image models suitable to a stereoscopic image do not exist. Although geometric relation between a depth and pixel disposal through normal refraction has been studied in the previous refraction stereo, such a model is not suitable for birefringence stereo given with a specific property of extraordinary refraction. The relation between the depth and pixel disposal by birefringence has not been formulated yet. In addition, the previous refraction stereo calibration method for a birefringent material has not been studied. Lastly, the previous refraction stereo finds a pair of images, that is, a direct image and a refracted image corresponding to each other. However, since the birefringence allows two overlapping refracted images to be combined into one image, a new corresponding searching strategy which is capable of processing overlapping information in an image is required.
Therefore, there is a need to provide a method capable of estimating depth information for a birefringent stereo.